Steel, a common material in modern machinery and consumer goods used for its strength and resistance to corrosion, is an alloy of iron and several other elements, such as carbon or silicon. Although all steel alloys contain iron, the proportion of other elements to iron depends on the type of steel. As a result, the molar mass -- a chemical measurement used to state the mass of a defined number of molecules of an element or compound -- of steel varies widely depending on the type of steel in question.

Molar mass is a measure of the mass of one mole of any element or compound. Defined by Avogadro's number, one mole is roughly equivalent to 6.02 x 10 raised to the 23rd, a huge number used to make the infinitesimal mass of a molecule a more practical value in applied chemistry. The molar mass of carbon, for example, would be the mass of 6.02 x 10 raised to the 23rd molecules of carbon. Molar masses are listed on the periodic table of elements under each element, and the molar masses of compounds derived from numerous elements, such as NaCl, can be calculated by adding the molar masses of the two molecules in the compound and multiplying the result by Avogadro's number.

Strictly speaking, chemical mixtures or alloys, because they involve the physical mixing of elements or compounds without bonding the parts at a molecular level, do not have a molar mass. That being said, all of the chemically discrete constituent parts of a mixture or alloy do have a corresponding molar mass, which can be calculated and used to approximate molar mass for applied calculations in fields such as engineering. As an alloy, steel does not have its own chemical equation, but each variety of steel is made of different percentages of elements. The molar mass of each of these elements, multiplied by the percentage of each element in the alloy and added together to account for 100 percent of the sample, can give you a general idea of what the molar mass of steel would be for theoretical consideration.

Given its wide range of uses, steel has a significant number of variations, each with its own distinct mixture of iron and other elements. Electrical (silicon) steel, for example, is an alloy containing about 97.6 percent steel, 2 percent silicon and 0.4 percent carbon. All types of steel, however, are predominantly made of iron, with almost all alloys containing over 75 percent iron and the vast majority containing over 90 percent of the element by weight. The varieties of steel used for structural building supports are usually over 99 percent iron. This diversity means physical attributes such as mass vary across types of steel, even though some generalizations are possible.

Due to the large percentage of iron contained in all types of steel, the molar mass of iron can provide a general approximation for the mass of steel as a hypothetical compound. According to the periodic table, the molar mass of iron is 55.845 grams/mole. In steel alloys containing less than 1 percent of other elements by weight, this measurement almost will provide the hypothetical molar mass of steel. In cases in which other elements play a larger role in the alloy, the numbers can be adjusted to reflect a certain percentage of other molar masses.